Pneumatic rubber tires intended for heavy duty service (heavy duty rubber tires) conventionally have a tread with a cap/base layered construction where the outer rubber cap layer contains the running surface of the tread and where the tread cap rubber layer elastomer is comprised primarily of natural cis 1,4-polyisoprene rubber and are therefore natural rubber-rich. Such tire treads often have a small amount of cis 1,4-polybutadiene rubber to promote resistance to treadwear for the tire.
Polybutadiene rubber is generally not considered as being suitable as a primary elastomer for heavy duty tire treads.
A challenge is therefore presented for evaluating whether a synthetic rubber, namely synthetic cis 1,4-polybutadiene rubber, may be used to replace a significant amount of natural rubber for such heavy duty tire treads and achieve a combination of suitable resistance to wear (abrasion resistance) with similar resistance to tear (tear resistance) for the tire tread rubber composition, which are desirable rubber composition properties for the heavy duty tread cap rubber layer and, also, with suitable processability of the uncured rubber composition for preparation of the tread. A specialized synthetic cis 1,4-polybutadiene rubber is evaluated for such purpose.
Such cis 1,4-polybutadiene rubber is considered herein to be specialized in a sense of differing from more conventional cis 1,4-polybutadiene elastomers.
In the description of this invention, terms such as “compounded rubber”, “rubber compound” and “compound”, if used herein, refer to rubber compositions containing of at least one elastomer blended with various ingredients, including curatives such as sulfur and cure accelerators. The terms “elastomer” and “rubber” may be used herein interchangeably unless otherwise indicated. It is believed that such terms are well known to those having skill in such art.